Conically threaded graphite anode stem with conductible plug



April 7, 197-0 W J. AN '1' VEEN CONICALLY THREADED GRAPHITE ANODE STEM WITH CONDUCTIBLE PLUG Filegi Oct. 12, 1966 V'VBVIUR. JAN VAN'T VEEN Y ML/MMM ATTORNEYS United States Patent Office CONICALLY THREADED GRAPHITE ANODE STEM WITH CONDUCTIBLE PLUG Jan van t Veen, Enschede, Netherlands, assignor to N.V.

Koninklijke Nederlandsche Zoutindustrie, Hengelo, Netherlands Filed Oct. 12, 1966, Ser. No. 586,201

Int. Cl. B01k 3/08 U.S. Cl. 204288 2 Claims ABSTRACT OF THE DISCLOSURE A graphite anode is provided comprising an anode plate having a threaded conical bore therein into which an anode stem comprising a graphite rod having a threaded conical end is in threadable engagement therewith. The stem has an axial bore in which is tightly confined a metal conductor, the stem having a conductible plug at its threaded end for making electrical contact with said conductor and said anode plate.

This invention relates a graphite electrodes and, particularly relates to an improved method and arrangement for coupling the graphite plate electrode to the stern used for mechanical support of and electrical coupling tosaid plate.

Plate-shaped graphite anodes, such as are in use in the alkali chloride electrolysis, are usually provided with stems or terminal rods or bars which are fixed in bore holes in the plates, which rods mechanically support the anode in the electrolytic cell and serve, at the same time, as lead-in conductors.

A commonly used form of anode stem is a graphite rod, threaded at one end. To attach the stem to the plate, the stem is screwed into a bore hole, tapped with corresponding threads, in the plate. At the other end of the stern rod, a metal pin is drawn axially to a certain depth into the rod and bonded to the rod by soldering. To prevent the penetration of the liquid electrolyte to the metal pin in the rod, the rod is impregnated with wax. Further, to avoid corrosion, the transition-seam between graphite rod and graphite plate is often coated with a protective lacquer.

One drawback to such construction is the relatively low conductivity of graphite. Also, at the transition from graphite rod to graphite plate, electrical resistance has invariably existed. Especially when high current densities are used in the electrolysis cells, such resistances significantly lower the efiiciency of the use of electrical energy.

It has also been proposed to use metal anode stems which are directly fixed in bore holes in the anode plates and which directly couple the current source to the plates.

For example, in U.S. Patent No. 2,627,501, an anode assembly is described wherein a metal anode rod is fixed in a threaded hole in the anode plate. To protect the metal from corrosion, the plate around the hole is impregnated with wax and a sealing sleeve is clamped tightlybetween the anode plate and a nut which is threadably engaged on the upper end of the anode rod. A drawback of this anode is the rather weak connection between the metal rod and the graphite plate due to the absence of mutual cohesion, the difference in hardness, and the different coefiicients of expansion of the difierent materials. Moreover, this =weak connection is initially loaded by the pressure of the clamping force on the sleeve.

It is, therefore, an object of the present invention to provide an improved method and arrangement for coupling a graphite plate to a stern in which improved mechanical and electrical coupling is provided.

According to the invention, the drawbacks of known Patented Apr. 7, 1970 anode assemblies are overcome by making use both of the good stability of the graphite rod screwed into the graphite plate and of the good electrical conductivity of the metal conductor which is brought into the bore hole of the plate. The bore hole in the plate is conical in form and the shape of the outer end of the graphite rod and the metal conductor which is axially carried through that rod is in such a way adapted to the form of that hole that by simply screwing the rod into the hole, at the same time a direct contact between metal conductor and plate and good enclosure of the bore hole against the penetration of liquid is obtained.

The invention is related to a plate-shaped graphite anode provided with an anode rod to conduct the electric current to the plate, characterized in that the anode rod comprises a graphite rod with an axial bore which is screwed into a conical bore hole in the graphite rod and by a metal conductor which is tightly connected with that graphite rod in the bore of that rod and extends into the bore hole in the plate and in that hole is provided with an enlarged end having an outline which is flush with the thread on the graphite rod.

The invention can in a simple manner be applied to existing graphite anodes provided with a graphite rod. Hereby the graphite rod has to be bored over the whole length of its axes then screwed into the threaded hole whereby always care should be taken that the underside of the rod keeps free from the botom of the hole, to ensure a good enclosureand thereafter, a molten metal or metal alloy is poured into the bore whereafter a metal core (e.g. a copper rod) is placed in the molten metal. After solidification of the molten metal, an anode assembly according to the invention, is obtained which simply can be applied in cells adapted to existing anodes, which assembly has the mechanical stability of the known anode plates with graphite rods and the good electrical conductivity of anode plates with metal lead-ins.

It is recommended that the plate around the bore hole be impregnated with a sealant before insertion of the stem. Such an impregnation, for example, can be carried out by pouring wax in the bore hole and heating the plate at a temperature higher than the melting point of the wax for several hours. The stem also will be impregnated before insertion in a suitable manner.

If a wax is used with a melting point lower than the melting point of the metal used for melting in, e.g., a parafiin wax with a melting point at about C. and a normal lead-tin solder, the melting-in process should be carried out within a short time and after putting in the metal rod, the assembly should be coated quickly in order to reduce the spreading-away of the wax. Use can be made of a high-melting wax, e.g. a chlorinated hydrocarbon, such as hexachlorobenzene and/or a low melting alloy, e.g. an alloy of lead and bismuth.

Having briefiy described this invention, the method and apparatus will be described in greater detail along with other objects and advantages in the following portions of the specification, which may best be understood by reference to the accompanying figure which is a cross sectional view of an anode and stem in accordance with the present invention.

In the single figure, there is shown a typical anode constructed in accordance with the present invention. For example, the anode might be utilized for alkali chloride electrolysis. The structure comprises a graphite anode plate 1 having a threaded conically shaped bore hole attached therein. The stem comprises a graphite casing 2 having a copper rod 3 conductively affixed to the axial bore in the stem 2 as by soldering. The solder is continued to form a solder plug 4 at the end of the stem. The stem casing is tapped in the end entering the bore hole with matching conical threads and the solder plug 4 is dimensioned to engage the outer surface of the threads in the anode plate when the stem is tightly turned into the bore hole. The thread engagement and axial length of the plug is controlled to prevent contact of the plug with the bottom of the bore hole when the stem is preformed as will be explained in detail hereinafter. When the stem is tightly engaged with the plate, the anode may be formed by pouring solder into the bore hole cavity and inserting the rod 3 into the molten solder. The plug 4 will then continue to the bottom of the bore hole.

While methods for constructing the stem will be explained in detail hereinafter, certain of the advantages of this construction might best be pointed out here. Since the stem tightly engages the threads in the anode plate (in the manner of pipe threads) and since, as mentioned previously, the plate and stem may be impregnated with wax, a very secure mechanical coupling is alforded to exclude penetration of the chemical solution to the metal components of the stem. This connection has been found to be maintained during use by virtue of the identity of the material in both the plate and the stern. Thus, the stem and plate have the same expansion characteristics and the mechanical coupling of the graphite stem to the graphite plate is properly maintained during operation.

Electrically, the coupling to the anode plate through the stem is considerably improved over conventional arrangements. It is found that there is a lower resistive drop at the junction between stem and plate than the solid graphite rod construction which lowered conductivity is not upset by penetration of the solution being electrolyzed and, thus, a low resistance is maintained throughout use.

Surprisingly, it has been found that the improvement in the conductivity of this new anode construction compared with the known graphite rod need not be ascribed to a direct contact of the metal conductor with the bottom of the bore hole in the anode plate.

From an anode constructed in the above said manner, the rod was screwed out of the plate. It appeared that a very tight connection between the graphite rod and the metal core and the metal (solder) plug at the underside of the core was formed. Now, enough metal was ground off the bottom of the plug so that, after screwing the rod again in the plate, no contact of the plug with the bottom of the hole in the plate was possible. In measuring the electrical conductivity, no decrease in conductivity was found. However, after grinding off the whole part of the metal conductor protruding from the underside of the graphite rod, an increase in electrical resistivity was measured.

In accordance herewith, it has been found to be possible to use one and the same anode rod in several anode plates in succession, whereby it is not necessary to repeat the melting-in process for every new anode plate. Only care should be taken that the depth of the new anode plate is large enough to prevent the metal conducting-disk to meet the bottom of the hole before the screwtap between rod and plate is closed.

Further, it is now made possible, according to the invention, first to carry out the melting-in procedure, for example, by using a mold with the form of the bore hole in the anode plate and thereafter to impregnate the rod with wax.

Preferably, the anode rod is made by using a mold, with a hole corresponding with the conical hole in the anode plate, having a depth large enough to make it possible that the rod is fixedly screwed into that hole without reaching the bottom but at the same time being somewhat shallower than the hole in the anode plate. The seam between the graphite casing and the metal conductor can be made by melting-in in the above said manner whereby in the room between the bottom of the hole and the underside of the graphite rod, a metal disk or plug is formed having at its outline a thread linking up with the thread on the. graphite rod. The metal pin is preferably put into the molten metal onto the bottom of the hole since in doing so, during the solidification of the solder, a particular tight connection between the dilferent parts of the anode rod is obtained. By screwing the anode rod so formed in the anode plate, the disk-shaped part of the metal conductor is pressed against the side wall of the conical bore hole whereby a very good direct electric contact with the anode plate is obtained.

For completeness of disclosure, but not by way of limitation, a typical construction is delineated.

In a graphite plate in the form of a graphite anode for an alkali chloride electrolysis, a bore hole is made with a bottom diameter of 6 cm., an upper diameter of 6.3 cm. and a depth of 2.8 cm. In the side wall of this hole, a thread is tapped with a depth of about 0.1 cm, and a pitch of 6 passes per 2.5 cm. The hole is filled with molten paraffin wax. The plate is heated at 20 C. during 24 hours and thereafter the remaining wax is removed from the hole.

In another graphite plate a bore hole is made, provided with a corresponding thread with the same upper diameter and the same slope of the side wall but with a depth of 2.6 cm. This plate is used as a mold in the construction of the anode rods.

In a cylindrical graphite bar with a length of 26 cm. and a diameter of 7.2 cm., an axial bore is made over the whole length of the bar, with a diameter of 3.6 cm. The end of the rod is provided with a thread exactly fitting to the thread in the bore hole of the plate when the rod is screwed in the plate so far that the distance between the bottom of the hole in the anode plate and the underside of the grahpite rod is about 0.7 cm.

The graphite rod is screwed into the mold. Mold and rod are heated to 320 C. A molten mixture of 33% lead and 67% tin is poured into the bore in the rod. A copper pin (diameter 3.4 cm. and length 30 cm.) is put into the bore of the rod onto the bottom of the bore hole in the mold. Care is taken to have sufficient solder in the bore to completely fill up the space between metal core and graphite casing. After cooling to room tempera ture, the rod is turned out of the mold and then in a normal manner, impregnated with wax. By screwing this rod in the anode plate, an anode construction according to the invention is obtained in an embodiment such as schematically is indicated in the accompanying drawing;

This invention may be variously modified and embodied within the scope of the subjoined claims.

What is claimed is:

1. In combination, a graphite anode comprising an anode plate having a threaded conical bore hole therein and an anode stem, said anode stem comprising a graph ite rod with an axial bore over the whole length of that rod, said stem having a conical end threadably engaged into said conical bore hole in the anode plate, said stem having an axial metal conductor which is tightly coupled to the graphite bar along the length of the axial bore therein, said stem being provided with a conductive plug on the threaded end electrically coupled to said conductor and threadably dimensioned to engage electrically the outer surface of the threads in said borehole when said stem is tightly threaded therein.

2. An anode stem for use with a graphite anode plate having a threaded conical bore hole therein, comprising a cylindrical graphite rod having an axial bore extending the entire length of said graphite rod, a metal conductor positioned within said axial bore and bonded to said bore in electrically conductive relationship thereto, one end of said rod being provided with a conical shaped threaded section adapted for engagement within said conical bore hole and a metal plug electrically coupled to said conductor and mounted on said threaded end of said stem, said metal plug being threadably dimensioned to engage electrically the outer surface of the threads in said bore hole when said stem is tightly engaged therein.

(References on follow ng page) References Cited UNITED STATES PATENTS FOREIGN PATENTS 365,815 1/1932 Great Britain.

Wheeler 204286 JOHN H. MACK, Primary Examiner Boothrnan 204286 ornhjelm 5 D. R. JORDAN, Asslstant Examlner Brown et a1. 204279 US. Cl. X.R. Shibata et a1. 204288 204294 

